Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with agraphical user interface showing the new design with environment inbroken lines.

The outermost broken lines illustrate the display screen or portionthereof and the broken line showing of text, numbers, symbols and iconsillustrate portions of the transitional graphical user interface. Noneof the broken lines form part of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface showing the new design, as shown anddescribed.